///////////////////////////////////////////////////////////////////////////
//                   __                _      _   ________               //
//                  / /   ____  ____ _(_)____/ | / / ____/               //
//                 / /   / __ \/ __ `/ / ___/  |/ / / __                 //
//                / /___/ /_/ / /_/ / / /__/ /|  / /_/ /                 //
//               /_____/\____/\__, /_/\___/_/ |_/\____/                  //
//                           /____/                                      //
//                                                                       //
//               The Next Generation Logic Library                       //
//                                                                       //
///////////////////////////////////////////////////////////////////////////
//                                                                       //
//  Copyright 2015-20xx Christoph Zengler                                //
//                                                                       //
//  Licensed under the Apache License, Version 2.0 (the "License");      //
//  you may not use this file except in compliance with the License.     //
//  You may obtain a copy of the License at                              //
//                                                                       //
//  http://www.apache.org/licenses/LICENSE-2.0                           //
//                                                                       //
//  Unless required by applicable law or agreed to in writing, software  //
//  distributed under the License is distributed on an "AS IS" BASIS,    //
//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or      //
//  implied.  See the License for the specific language governing        //
//  permissions and limitations under the License.                       //
//                                                                       //
///////////////////////////////////////////////////////////////////////////

/**************************************************************************
 * Copyright (C) 2012 - 2014 Armin Biere JKU Linz
 * <p>
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to
 * deal in the Software without restriction, including without limitation the
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * <p>
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * <p>
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 ****************************************************************************/

package org.logicng.collections;

/**
 * A simple priority queue implementation for elements with long priorities taken from CleaneLing.
 * @version 1.3
 * @since 1.0
 */
public final class LNGLongPriorityQueue {

  private final LNGIntVector heap;
  private final LNGLongVector prior;
  private final LNGIntVector pos;

  /**
   * Creates a new priority queue.
   */
  public LNGLongPriorityQueue() {
    this.heap = new LNGIntVector();
    this.prior = new LNGLongVector();
    this.pos = new LNGIntVector();
  }

  /**
   * Returns the left position on the heap for a given position.
   * @param position the position
   * @return the left position
   */
  private static int left(int position) {
    return 2 * position + 1;
  }

  /**
   * Returns the right position on the heap for a given position.
   * @param position the position
   * @return the right position
   */
  private static int right(int position) {
    return 2 * position + 2;
  }

  /**
   * Returns the parent position on the heap for a given position.
   * @param position the position
   * @return the parent position
   */
  private static int parent(int position) {
    assert position > 0;
    return (position - 1) / 2;
  }

  /**
   * Returns whether the queue is empty or not.
   * @return {@code true} if the queue is empty, {@code false} otherwise
   */
  public boolean empty() {
    return this.heap.empty();
  }

  /**
   * Returns the size of the queue.
   * @return the size of the queue
   */
  public int size() {
    return this.heap.size();
  }

  /**
   * Returns whether a given element is already imported and present in the queue or not.
   * @param element the element
   * @return {@code true} if the element is already imported and present in the queue, {@code false otherwise}.
   */
  public boolean contains(int element) {
    return element >= 0 && this.imported(element) && this.pos.get(Math.abs(element)) >= 0;
  }

  /**
   * Returns the priority for a given element.
   * @param element the element
   * @return the priority of the element
   */
  public long priority(int element) {
    assert this.imported(element);
    return this.prior.get(Math.abs(element));
  }

  /**
   * Returns the top element of the priority queue (= the element with the largest priority).
   * @return the top element of the priority queue
   */
  public int top() {
    return this.heap.get(0);
  }

  /**
   * Pushes a new element to the queue.
   * @param element the element
   * @throws IllegalArgumentException if the element to add is negative
   */
  public void push(int element) {
    if (element < 0)
      throw new IllegalArgumentException("Cannot add negative integers to the priority queue");
    assert !this.contains(element);
    this.doImport(element);
    this.pos.set(element, this.heap.size());
    this.heap.push(element);
    assert this.heap.get(this.pos.get(element)) == element;
    this.up(element);
  }

  /**
   * Updated the priority of a given element.
   * @param element  the element
   * @param priority the new priority
   */
  public void update(int element, long priority) {
    this.doImport(element);
    final long q = this.prior.get(element);
    if (q == priority)
      return;
    this.prior.set(element, priority);
    if (this.pos.get(element) < 0)
      return;
    if (priority < q)
      this.down(element);
    if (q < priority)
      this.up(element);
  }

  /**
   * Removes a given element from the priority queue.  Its priority is kept as is.
   * @param element the element
   */
  public void pop(int element) {
    assert this.contains(element);
    int i = this.pos.get(element);
    this.pos.set(element, -1);
    int last = this.heap.back();
    this.heap.pop();
    int j = this.heap.size();
    if (i == j)
      return;
    assert i < j;
    this.pos.set(last, i);
    this.heap.set(i, last);
    this.up(last);
    this.down(last);
  }

  /**
   * Removes the top element from the priority queue.
   */
  public void pop() {
    this.pop(this.top());
  }

  /**
   * Compares two elements by their priority and returns whether the first element's priority is less then the second
   * element's priority.
   * @param e1 the first element
   * @param e2 the second element
   * @return {@code true} if the priority of the first element is less than the priority of the second element
   */
  private boolean less(int e1, int e2) {
    return this.prior.get(e1) < this.prior.get(e2);
  }

  /**
   * Bubbles a given element up.
   * @param element the element
   */
  private void up(int element) {
    int epos = this.pos.get(element);
    while (epos > 0) {
      int ppos = parent(epos);
      int p = this.heap.get(ppos);
      if (!this.less(p, element))
        break;
      this.heap.set(epos, p);
      this.heap.set(ppos, element);
      this.pos.set(p, epos);
      epos = ppos;
    }
    this.pos.set(element, epos);
  }

  /**
   * Bubbles a given element down.
   * @param element the element
   */
  private void down(int element) {
    assert this.contains(element);
    int epos = this.pos.get(element);
    int size = this.heap.size();
    while (true) {
      int cpos = left(epos);
      if (cpos >= size)
        break;
      int c = this.heap.get(cpos);
      int o;
      int opos = right(epos);
      if (!this.less(element, c)) {
        if (opos >= size)
          break;
        o = this.heap.get(opos);
        if (!this.less(element, o))
          break;
        cpos = opos;
        c = o;
      } else if (opos < size) {
        o = this.heap.get(opos);
        if (!this.less(o, c)) {
          cpos = opos;
          c = o;
        }
      }
      this.heap.set(cpos, element);
      this.heap.set(epos, c);
      this.pos.set(c, epos);
      epos = cpos;
    }
    this.pos.set(element, epos);
  }

  /**
   * Returns whether a given element is already imported.
   * @param element the element
   * @return {@code true} if the element is imported, {@code false} otherwise
   */
  private boolean imported(int element) {
    assert 0 <= element;
    return element < this.pos.size();
  }

  /**
   * Imports a given element.
   * @param element the element
   */
  private void doImport(int element) {
    while (!this.imported(element)) {
      this.pos.push(-1);
      this.prior.push(0);
    }
  }

  @Override
  public String toString() {
    final StringBuilder sb = new StringBuilder("LNGLongPriorityQueue{");
    for (int i = 0; i < this.heap.size(); i++) {
      sb.append(String.format("<elem=%d, pos=%d, prio=%d>", this.heap.get(i), this.pos.get(i), this.prior.get(i)));
      if (i != this.heap.size() - 1)
        sb.append(", ");
    }
    sb.append("}");
    return sb.toString();
  }
}

